Vacuum leak decision

I bought a 2002 996 Carrera 2 cab, 6 speed in September�..first time Porsche owner. Loving it so far. I�ve done lots of car work in the past, but since this is my first Porsche, I could use some advice. I�m chasing goofy / non-linear throttle response below 3000 rpm at partial throttle (high vacuum). The engine isn�t missing, but it hesitates very slightly when pulling away from a stop or it sometimes surges slightly when I push down on the throttle just a little. None of these symptoms are severe�.but it�s enough to take away from the otherwise fantastic driving experience this thing gives me. I�ve covered the basic maintenance so far: - fresh oil - new plugs - new coils - new O2 sensors - new water pump - new motor mounts - new throttle body (not routine maintenance�.but it was cheap enough, and I was chasing goofy throttle response, so I replaced it). All parts are from FCP euro and are OE or OEM. Everything I did made it better, but it�s still not fixed. I bought a smoke tester and checked for vacuum leaks�..and found a few (see pictures). One leak that is at the elbow of some sort of breather tube above the alternator. (picture attached with red arrow) One leak from something on the passenger side close to where the manifold bolts to the head. This passenger side leak is coming from something that looks like a vent. (picture attached with red arrow�but the part in question is blurry) One leak from the drivers side below the alternator. I can�t pinpoint this one yet but it seems like it�s coming from somewhere along the intake runner or where the intake bolts to the head. (picture attached with red arrows) One leak from the top of the manifold, behind the throttle body, from what I think is the damper or some sort of flap internal to the intake. No picture on this one. Questions: -What is the name of the breather elbow above the alternator? -What is the name of the thing that looks like a breather / vent close to the passenger side cylinder head? -Any thoughts on what could be leaking below the alternator? �..and finally�.. Am I just getting to the point where I need to bite the bullet and drop the engine and take the time to �reseal� the leak prone items in the intake system? All the pictures were from when I was smoke testing but the smoke didn�t show up very well. I put arrow to show where I was having leaks. Don�t blame me for the headlight covers�they were on there when I bought it Elbow Breather / vent on passenger side�.zoomed out Breather / vent on passenger side�.zoomed in) Leak from below alternator.

I like to use the visual parts catalog at AutoAtlanta. It�s great for finding parts when you only know what it looks like. http://www.autoatlanta.com/porsche-p..._911_parts.php Edit: if you do decide to drop the engine, there�s a bunch of stuff you ought to do while you�re there. such as: fuel injectors, AOS (I would recommend the UAOS), VarioCam wear pads, chain tensioners, etc. maybe even the IMS, too�

Elbow above alt is brake booster vacuum. Very common leak, rescue tape is effective. part on pass head is AOS vent valve. The check valve is likely stuck. resonance flap is behind throttle body. Usually leaks from the pivot on the front, there is a vacuum line in back that can get disconnected also. Access is via removing the TB and plenum. dunno what the other leak near alt is. It�s a little work but by no means does addressing these require dropping the engine

Leak behind the alt could be the oil fill tube or one of a multitide of vacuum lines that are behind it. Remove the alt and re-smoke to narrow it down.

Thanks for the reply�s, they were both helpful. Looks like I can just tape up the brake booster elbow. I�ve read of a few people using a 3/4� ID vacuum cap to seal over top of the resonance flap�..which seems pretty straightforward. Seems like I can clean or replace the AOS breather. fixing these address the biggest leaks and hopefully resolve my throttle response issue. The one below the alternator is the smallest leak. I�ll dig into that one a little more and hopefully fixing that doesn�t require pulling the intake. if it does require significant work (like pulling the intake), I�ll likely postpone fixing that one until the winter or whenever I want to bite the bullet and drop the engine to do the full treatment of injectors, AOS, IMS (mine is original with 102,000 miles), etc.

U can reach all the vac lines if u remove the alt. There is decent access. What u really need to do is test the aos if the breather is wet. I would put this at the top of the 2 do list. It requires an manometer and a fitting screwed into an extra oil cap. There is nothing to fail in the breather elbow, its a one way flap that is allowing excess crank case vapor to expel. Most likely caused by a failed aos or a very loose engine. The aos being the issue 99 of 100 times.

Sorry in advance for the verbosity�.i�m feeling wordy today. I think I made things better�.can�t tell yet since I�ve only taken one test drive and the computer hasn�t gone through its learning cycle yet. Following the good advice, I pulled the alternator to continue trying to pinpoint the vacuum leak. After I pulled the alternator, I then, well, while I�m in here, might as well pull the throttle body and crossover tube so I can put a vacuum cap over the damper pivot shaft that was leaking. So I took off the throttle body and crossover tube�..then said, well��the starter is right there�.and my starter bendix hangs almost all the time in cold starts��so I pulled the starter. Struck out with the starter. I couldn�t get the solenoid torx screws to break free, so I couldn�t take the solenoid off to lube anything I settled for just spraying the bendix from the outside with PB Blaster. Don�t think it�ll do anything since there�s a seal there�..I�m betting my bendix will continue to hang on cold starts. Oh well�..back to the vacuum leaks. Pulled the oil breather from the passenger side cylinder head. In my original post, I forgot to mention that the leak I saw from the breather was from where the breather seats into the head. It wasn�t leaking from the check valve / vent area. That thing was a real pain in the but to remove / replace. I tried to find a new O-rings for the breather but didn�t have the right size on hand. I admitted defeat and put the old O-rings back in��darn. I put a very very thin film of RTV silicone above the O-ring on the breather-to-cylinder head mating surface. I used a tiny bit of RTV so hopefully I won�t pay a penalty for that later. I taped up the brake booster elbow. I reassembled all the intake and vacuum components and smoke checked again before installing the alternator. brake booster elbow leak fixed. Breather leak fixed. Intake crossover resonance flap leak fixed I located the source of the smoke I originally mentioned was coming from below the alternator. The drivers side middle fuel injector has a small vacuum leak. It�s not too big�.and I wasn�t diving in that far�..so fixing that sucked will have to wait until this winter (or some future winter) when I pull the engine to do injectors, AOS, IMS�..all that stuff. I also broke the plastic nipple / bracket for the small coolant hose to the right of the alternator. It was very brittle so good thing it happened now instead of on the road somewhere. Didn�t have a replacement part so I used a metal nipple from Doorman to join the hoses until I can get the right replacement part. So in summary, I fixed all but the injector vacuum leak. During the test drive, it felt great. The goody throttle response was not really noticeable. Time will tell if the problem is actually better or if it will return as the computer goes through its learning cycle. I didn�t mention in my original post (but you�ll see in the pictures) that I have an aftermarket airbox and a K&N air filter. This setup came with the car. I�ve cleaned and oiled the filter. Eventually this setup may have to be replaced by a stock air box if the goofy throttle response comes back. For now, I�m just enjoying the nice intake sound it gives me On a side note�..man this thing is fun. Modulating the throttle in corners and doing the under steer / oversteer dance is fun as could be with the great steering feel and response this thing has. I also have an NB Miata with coilovers that is a blast on the same roads�..but this 996 is just a different kind of fun Might as well pull lots of stuff apart while I�m in here Failed attempt at lubricating the bendix. Stinkin brittle plastic. Luckily I had the tapered cone from the RTV to use as a plug after it snapped. Temporary fix for the snapped coolant hose nipple. If you look close at the injector, you can see dark coloring indicating a slight leak. I was also able to see proof positive smoke coming out when I smoke tested. Luckily the leak isn�t too big�..so hopefully I�m ok until the winter. All done for now.

Ditch the K&N oil filter and get a OE paper air filter box. Those have been notorious for causing problems with throttle response, and over oiling the filter gums up the MAF sensor.

If you like the cone filter (I think they produce a really aggressive sound), you can look for one by �aFe Power�. They make a variety of universal air filters that don�t require oiling.

great job!

I have the exact same throttle response issue, along with horrible fuel economy. Did a smoke test and found vacuum leaks at the same elbow piece and resonance tube as your car. Going to replace both parts next week!

After a few trips, I think things are a bit better but I still have some goofiness in the throttle. It�s not much but it�s just enough to annoy me. I went ahead and ordered a stock airbox and filter�.we�ll see if that fixes it. for the record, I never had a poor fuel mileage issue. Also, for the complete story: I took out the clutch helper spring when I first got the car since I really didn�t like the clutch feel with that helper spring in place. I didn�t realize at that time that there was a microswitch that sensed whether the clutch had been pushed in at all. when I took the helper spring out, I liked the clutch but had all sorts of bad throttle response. Reason: without the clutch helper spring, the micro switch was sometimes closed and sometimes open�..and I learned later that the switch affected throttle response / ignition timing. I then taped that switch so the computer always thinks the clutch is not depressed�..throttle response was waaaayyyy better�.but still had the slight non-linear response that I�m currently chasing. we�ll see if the stock airbox makes things better.

That coolant connector always breaks. You just look at it sideways and it breaks. There are alloy aftermarket replacements. Plenty of threads. Good to have it replaced although many just get by with a nipple configuration like you have.

Woo, don't know if you have aftermarket software on your car, but it can substantially improve your throttle response on a 996.2.

Many have run the K&N style filters but its the Plumbing that causes the problems, suposedly the stock airbox has a better flow curve and give more space between the MAF and the Throttle plate... YMMV I've run the K&N style that fits in the stock airbox and my Durametric showed similar MAF numbers to stock with paper.. WIth my new motor I'm running a stock air box with paper.. Again YMMV Enjoy the car they are just too much fun.

@woo102 How did you get the resonance tube out? Did you have to loosen the driver's side intake manifold to get the necessary clearance to wiggle it free? Contemplating my next move here.

@smith365film i did not have to losen the intake. FCP Euro has a pretty good video showing how to remove everything. You Tube

Gettkng it back in is worse . Use an inspection mirror or even better, a endoscope to confirm the boots r on correctly. Most swear they get it right but dont.

Quotes source post: 19472353

I just went through all of these issues after discovering oil leaking from the crossover tube from the AOS( and all the havoc that it caused ). I ultimately went to the UAOS as a replacement for stock which have a high failure rate. You probably have a failed one also�replace asap. This job can be done with a motor drop as opposed to motor out. Yes removing intakes makes it all easier to get to resonance tubes�etc. Any work on these 20 something�s will reveal brittle plastic pieces and they will create Vac leaks as well as installer error( yea�that�s it most of the time�Ask Skip�designer of the UAOS. One of the coolant lines modified during the install failed and that caused lot of issues with coolant contamination. Car was idle so long can�t get system ready due to O2 sensors and cats so still chasing that. I have an p0174 that�s most likely needing a new MAF sensor. I�m going to check the live date on the Durametric and confirm if value# are off again. Patience is your friend and not over-thinking solutions�great work so far.You�ll get it.

Yeah, they unbolt the intake manifold in the FCP Euro video. Happy to hear that it's possible to remove (and maybe reinstall) without doing that extra work. I can locate the 6 manifold bolts with my fingers, but there's no way I'm getting a socket or wrench on the back one without at least pulling the alternator out.

Okay, I was able to remove it. Looks like Pelican Parts sold me the wrong replacement resonance tube, though. Where is everyone finding this replacement part? The smaller Boxster version of the tube seems to be the only one readily available.

The stock airbox I ordered off of eBay came in�..but��my car developed a problem: Very hard starting. I week or two before I went on the vacuum hunt, the car did something funny. I stopped to get something to eat. When I came back out, the car started fine and I drove away fine. 5 minutes down the road, the car bogged, stumbled hard, and lost most of its power�..thought I was going to have to pull over and get a tow. Then it cleared up and ran fine for a couple weeks. Then I went on this vacuum leak hunt. The car ran better when I was done with the vacuum leak hunt�..but I started noticing it would crank over slightly longer than before, before it actually started. At the time, I chalked it up to computer re-learn after the battery was disconnected. The extended cranking when starting problem got progressively worse�.and today, it will barely start. If I leave the gas pedal alone, it won�t start at all. If I try to start at WOT, it won�t start at all. I have to feather the throttle to get it to start. Then it stumbles for a bit. Then it runs absolutely stinkin fine. No black smoke at all when this happens�.so I don�t think it�s rich / flooding. I got out my cheap OBD2 dongle and read the RPM while cranking. I was getting ~200 rpm while cranking, so I don�t think it�s a crank sensor. Going to check the fuel pressure while cranking tomorrow and see what I find. Maybe it�s a bad fuel pump and / or fuel pump relay.

Sounds like your guess is good,,,, first thing I thought of was a fuel pump. Second was a bad ignition switch... Third was your engine block to chassis ground, on the passenger side bottom of the motor, when I dropped my engine to replace it, found that cable was loose.. and covered in oil and dirt. Perfect hatching ground for a intermittent ignition shutdown.

Fuel pressure update: Hooked up a fuel pressure gauge. Car was cold. Cycled the key on and off 3 times: gauge got up to around 18 psi once, immediately leaked down to 0 in about 3 seconds and struggled to even move the second time I tried to cycle on/off 3 times. When trying to start the car, the pressure while cranking was between 10 psi and 18 psi. The car started (a bit of an extended crank time but not bad at all) and the pressure was up at 48-50 psi. Shut the car off and the pressure leaked down to 0 in less than 10 seconds. Started the car again and got the same results. Time to order a fuel pump and relay.

Something else to check out and replace, the fuel pressure regulator. Might be leaking and bad.

Probably not the fuel pump but the regulator, me thinks.

Also could be the flexible lines in the fuel tank.

Quotes source post: 19488079

Yes, don't forget those. My understanding is the only way to know is to look at them directly. Not uncommon for them to split. At this point are they available separately from the fuel pump or is it all one unit?

Quotes source post: 19488289

Amazon has the the coragated vinyl fuel lines in all kinds of shapes and sizes if u need to make a repair.

Finally got the fuel pump in: problem solved. Before taking it for a test drive, I tested the fuel pressure and leak down. Pressure was around 48-52 while running lost less than 5 lbs in 10 minutes. Took it out for a few drives�..did a few hot starts�..works great! The only hiccup I ran into was the fuel float/sender. Even though everything I read said because to ensure the float if moving free (not tangled up in lines) before finishing the instal, you guessed it, my fuel float was tangled in the lines and I was stuck on empty even after I put fuel in it. When I did the fuel pump, I emptied the fuel out of the tank first. I pulled the sender back out (this time with the fuel tank mostly full) and made sure it was free before reinstalling. 2nd time was a charm. The new fuel pump hoses were routed slightly differently (see picture)�.not sure why. Next thing is to put the stick air box on.

Another update. I haven�t put the stock airbox back on yet. I did reconnect the clutch pedal switch�.the one that senses whether or not the clutch pedal is all the way at the top. After driving around like that for a few days, I�d say most of my driveability problems are solved. I think I had a combination of things going on that all had to get resolved before the drivability problems went away. Ever since I�ve had the car, I haven�t liked the throttle response / drivability�..it was non-linear. I wasn�t happy with clutch feel either�.so I took the clutch helper spring out. That put me in a bad situation where sometimes the clutch pedal returned fully and depressed the switch and sometimes it did not�..which made the drivability worse and inconsistent. I bypassed the switch and made thing a bit better but still not great. I fixed the vacuum leaks which made things slightly better but still not good enough. I installed a lighter clutch helper spring which made the clutch feel a lot better AND returned the clutch pedal fully every time. and finally, when I reinstalled the clutch pedal switch, the culmination of all the fixes was realized. I�d call it fixed. I think the fuel pump was just coincidence and did not impact the resolution of the drivability issue. As a side note, if you bypass the clutch switch (tape it in the �depressed� position), it will make your cruise control stop enabling / working. During this process, my cruise control green dash light stopped coming on. Once I put the clutch switch back in place, the green cruise control light started coming on again and the CC started working again. I guess the computer figured out the clutch switch has not changed in multiple trips and disables the cruise control. Now that drivability is straightened out, next stop for this car is Tail of the Dragon! I just took my Miata down there for the weekend and had an absolute blast. Can�t wait to take the 996.

What was the lighter clutch helper spring that you ended up installing?

The clutch helper spring for 996 Turbo is a very light spring because 996 Turbo uses a hydraulically assisted clutch. It seems to be the go-to for a light 996 clutch helper spring. Every other 996/986 uses exactly the same clutch helper spring.

I used a generic spring from Home Depot. Sorry�..I looked around and can�t find the part number for it. I originally found the part number in a thread somewhere on rennlist. the spring was just strong enough to fully return the pedal and I didn�t lose any clutch feel.

I was cleaning out the garage and found the spring I used